I have no animus towards possums, despite the fact that they always seem to try to shit on my head for trying to save their life by putting them up a tree.
And possums do have some marvelous features such incredible fecundity, almost complete immunity to rabies, and immunity to cotton mouth and rattlesnake bites.
That said, possum shit can ruin a lot of barn hay, and these animals can carry a brain worm that is dangerous to horses (as can barn cats, it should be said).
As for the notion that possums are capable of reducing the tick load in an area, that is complete hokum. Ticks breed at a rate that is astounding even for possums, and possums make no serious dent in tick numbers. Sorry.